Indonesia confirmed it’s closer to reaching an almost $4 billion agreement to take control of Freeport-McMoran Inc.’s giant Grasberg copper and gold mine after more than a year of negotiations.

Talks between state-owned PT Indonesia Asahan Aluminium, known as Inalum, Freeport and Rio Tinto Group have been completed and an agreement could be signed as early as this week, Indonesia’s State-Owned Enterprises Minister Rini Soemarno and Deputy Minister Fajar Harry Sampurno said on Saturday. On Monday, Freeport shares fell along with copper prices.

“We are finalizing the necessary documents,” Soemarno told reporters in Jakarta. “They are asking for stability in investment. They want to have documents that provide clarity in investment calculations, clarity in tax. These are all being processed.”

Their comments came after Inalum Chief Executive Officer Budi Gunadi Sadikin said last week that negotiations were complete and the parties have agreed a price for Rio’s stake.

The London-based company is ready to accept a $3.5 billion deal for its interest in Grasberg, people familiar with the discussions said last month.